**14. SIAE gene and SLE**

Cd22 - also known as SIGLEC2 - is a lectin that belongs to the sialic acid binding immunoglobulin-like lectin family. It is expressed by B cells and functions as a negative regulator of B cell activation. Accordingly, deficiencies of SIAE and CD22 produce phenotypes characterized by hyperactive B cells and spontaneous autoimmunity as in SLE in animal models. In fact, exon sequencing of the SIAE gene in a small group of patients with high titers of antinuclear antibodies (13 of whom had defined autoimmune diseases) found that 2 out of 19 had rare loss of function variants of SIAE. Loss of function alleles was found to be more common in patients with autoimmune diseases [27].
